1. Field of the Invention
The present invention relates to an apparatus and method for the manufacture of sliders used in magnetic storage devices. More particularly, the invention relates to an improved system for controlling the amount of non-linear deformation in wafer quadrants of slider rows during lapping in manufacturing.
2. Description of the Background Art
Digital magnetic disk drives are one very widely used type of storage device today. Such drives employ head-mounted magnetic transducers to read and write data on rotating disk media. The operable portion of such a transducer head is called a "slider," and the key operational portion of a slider is a transducing gap between pole elements. It is the characteristics of this gap, which to a large degree, determine the performance of the slider, and ultimately its suitability for use in a disk drive.
Most dimensions of a slider's gap are dictated by the semiconductor-type fabrication processes used, and are therefore generally not a problem, since such processes can be very precise. A critical exception, however, is the depth of the gap, termed "stripe height" for magneto-resistive heads (the present discussion also may apply to inductive heads, where the usual term used is "throat height"). The stripe height is achieved by abrasively removing material in a lapping step during manufacturing.
Problems arise with regard to the stripe height because sliders are typically manufactured together in batches. A number of such rows of sliders are deposited together onto a single semiconductor-type wafer, which is then cut into pieces commonly termed "wafer quadrants" (or just "quadrants"). A wafer quadrant is bonded onto an extender tool (also sometimes known as a row tool, transfer tool, or support bar) and the foremost slider row is lapped as a unit on an abrasive surface, such as a plate coated with an appropriate slurry mix. The slider row is then cut from the wafer quadrant, so that lapping of a new foremost slider row may commence. The sliced off row of sliders is ready for additional manufacturing steps, dicing into individual sliders, and then the final steps which ultimately produce working disk drive heads.
Unfortunately, lapping of a slider row as a unit can produce variation in the various slider's stripe heights. For example, even if a slider row is perfectly linear, it needs to be lapped in true parallel against the lapping surface, or sliders at one end of the row will be lapped differently than those at the opposite end. This is commonly referred to as "balance," and it is a problem which the industry has long appreciated and has generally developed adequate methods to correct.
Of present interest is where the foremost slider row in a wafer quadrant is not linear. The stresses inherent in wafer material and in the operations of lapping and slicing can all produce varying degrees of concave, convex, and higher order curvatures. This non-linear deformation is commonly termed "row bow" (although the term "bow" is often an understatement of the actual non-linearity which may be present). If such non-linearity is not corrected before lapping, and preferably also dynamically during lapping, the individual sliders within a row will have different amounts of material lapped away, i.e. end with different stripe heights.
Various systems for the correction of such bow have been tried. U.S. Pat. No. 4,457,114 discloses a carrier having a support bar to which a slider row workpiece is bonded. The support bar is connected to a base portion of the carrier by a central stem portion and thermal expansion is used between opposite ends of the support bar and the base to control the shape of the support bar. To get a range in shape from convex to flat to concave, the support bar may be made to be convex when cool.
U.S. Pat No. 5,117,589 discloses a transfer tool having a longitudinal slot or chamber in which a piezoelectric actuator or screw is present to control the shape of the transfer tool. To get a range in shapes, this transfer tool may also be convex when the actuator is off.
U.S. Pat No. 5,203,119 discloses a transfer tool secured in a bow yoke holder. The transfer tool has a single central slot in which the end of a piston is captured. Upward movement of the piston causes the transfer tool to assume a convex shape, and downward action of the piston produces a concave shape.
U.S. Pat. No. 4,914,868 discloses a holder having an elongated longitudinal slot which defines a beam portion of the holder. An actuator applies pressure in the middle of the beam to deflect it in a manner producing a quadratic curvature. Separate actuators at either end of the holder are used to control balance.
U.S. Pat. No. 5,525,091 discloses a transfer tool which has an elongated longitudinal slot defining a beam. Actuators (of undefined nature, but implicitly electrically operated) are used to controllably press three pins against the beam such that the shape of a slider row bonded to the transfer tool is changed.
U.S. Pat. No. 5,607,340 discloses a row tool having a series of bend openings and stress relief openings. The openings are all disclosed as being generally quite proximate to the edge of the row tool to which a slider row is bonded. Related U.S. Pat. No. 5,620,356 by the same inventors discloses the system for operating this row tool. A pair of electromagnetic actuators are used to apply balance pressure and a set of three other electromagnetic actuators are used to apply rotational twist to the bend openings in the row tool. The noted structure and location of the openings dictates that the application of rotational twist is also proximate to the edge of the row tool where a slider row is bonded.
The last example presented above represents the most sophisticated prior art known to the inventors, but even it has severe limitations. Such limitations particularly include the intricate complexity of the row tool's shape, due to the number and placement of the openings, and the high difficulty of controlling all of the forces which must be applied together in concert to effect bow correction. Viewed as a vector sum, the use of rotational twist is effectively a simultaneous application of force in a direction normal to the lapping surface, along with lateral force. The normal forces applied from the three twist actuators can thus combine with the desired normal forces applied by the two balance actuators such that controlling the net forces throughout is quite difficult.
It is, therefore, an object of the present invention to provide an improved method, and apparatus for use of that method, for lapping sliders. Other objects and advantages will become apparent from the following disclosure.